In the genesis of automotive manufacturing, vehicle bodies were carriages fabricated from wood and leather. Hence the term “horseless carriage” came to describe automobiles. Subsequently, vehicles were developed having a steel frame chassis which was connected with the drive train of the vehicle. A steel vehicle body was then mated with the chassis.
Initially, steel vehicle bodies were connected together primarily by rivets and threaded fasteners. Welding was not an option in many situations since the sheet metal was too thin to absorb the heat of most welding techniques. In the mid-20th century a welding technique was developed which could weld together relatively thin overlapping members of sheet metal, commonly referred to as spot welding.
In spot welding, a weld gun compresses a small portion of a joint of overlapping workpieces of sheet metal and applies pressure. Thereafter, an electric charge is delivered through the joint. The joint is heated until the metal of the joint is partially melted. The electric charge is stopped and the joint is allowed to cool wherein the metal of the two sheet metal workpieces is fused together.
The development of spot welding facilitated a tremendous advancement in vehicle body design. Now, structural components of the body could be fabricated from sheet metal which was folded into a desired tubular or other structural form, and then be welded together to form a structural beam. Therefore, the utilization of heavier plate members to provide the structural components of the vehicle body could be minimized.
Initially, most spot welding of vehicles was performed with equipment that could be either manipulated manually or via manual controls. In the early 1980s more and more equipment became available so that the spot welding function could be done robotically. Typically, the process lines that form a body are referred to collectively as a body shop and are part of an assembly plant. The body shop typically receives stamped workpieces from a stamping facility, which may be an on-site facility or a plant that is distantly located and serves several assembly facilities.
Typically, each vehicle line has its own body shop. When an automotive vehicle is updated for a major redesign, the body shop is typically scrapped and a new body shop is built from scratch within the assembly plant facility. The paint shop of an automotive vehicle assembly plant which receives the body, typically is utilized over and over again. However, the body shop is typically rebuilt and is therefore a tremendous consumer of tooling capital. This expenditure of tooling capital not only reduces profits, but also discourages model changeover. The lack of model changeover often causes a lack of consumer demand. Therefore, body shop capital costs generate a vicious cycle which can lead to very negative financial results for a vehicle manufacturer.
Another reason why the body shop consumes a large amount of capital is that the body shop has typically been customized to a given vehicle. Therefore, in most instances vehicles that are dissimilar in size and function cannot be made on a common body process line. Even vehicles that are the same, but are built in geographically separated assembly locations typically have different body process lines since the process lines are typically built to accommodate a specific assembly plant.
The lack of flexibility of body process lines not only leads to increased capital cost, but is also less efficient in the utilization of maintenance equipment and purchasing. Maintenance and the associated training cost of operational personnel is also increased. Attempts have been made to provide more flexible equipment, but most of these attempts have dwelt on variation in the path programming of robotic operations and the utilization of robots whose end effecters can be modified. This has generally not saved money and time.
It is desirable to provide a process line where the process line can accommodate a vehicle after a major redesign with a minimum capital cost.
It is desirable to provide a process line with greater flexibility so that a wider range of vehicle bodies can be processed on the same processing line.
It is desirable to provide flexibility in the processing line such that it may produce different vehicles, such that the vehicles can be made sequentially with each other and not require a major maintenance operation to change over the tooling.
It is desirable to provide a process line wherein engineering, maintenance, training and purchasing costs can be reduced.